The present invention relates to photographic copying machines in general, and more particularly to improvements in means for regulating the intensity of copying light in photographic copying machines. Still more particularly, the invention relates to improvements in means for regulating the intensity of copying light in photoelectrically controlled copying machines with automatic regulation of exposure time, wherein a light intensity controlling arrangement is provided which controls the intensity of light which travels from a light source to a copying material.
Commonly owned German Pat. No. 1,162,192 discloses a photographic copying machine wherein an adjustable diaphragm is installed in the path of copying light. The diaphragm is adjusted in dependency on light transmissivity of the original to be copied in such a way that the intensity of copying light in the copying plane is maintained at a predetermined value. Such analog follow-up control systems are quite complex and expensive. In addition, the relatively high expenditures for such regulation are unnecessary because the quantity of copying light is regulated in any event as a function of time.